Hubble images

This galaxy cluster has provided some of the best evidence found for the existence of dark matter. Known as the Bullet Cluster, it was formed when two smaller galaxy clusters collided with more energy than any other known event since the Big Bang.

The Antennae Galaxies/NGC 4038-4039. These two spiral galaxies began to collide about 300 million years ago. They are some of the youngest and nearest colliding galaxies, giving astronomers one of their best opportunities to study the phenomenon. It may be a preview of what will happen when our galaxy runs into the Andromeda galaxy in a few billion years.

This image captures light from the eruption of the star V383 Monocerotis seven years ago. The light has been echoing through a cloud of dust around the star. Because the light bounces around the dust, it takes a much longer time to reach Earth from 20,000 light-years away.